Traditionally, it has been allowed release exhaust gas from marine vessels into the atmosphere with little or no post combustion treatment to reduce the emission of environmental deleterious constituents. International Maritime Organization (IMO) and several governments have implemented regulations that will prevent vessels not fulfilling minimum requirements for emission from operating. These legislations have forced ship owners to look for solutions for fulfilling the requirements, not only for ships to be built but more importantly for the current fleet of vessels.
Of special interest is emission of sulphur oxides (SOx) and particles formed by the combustion and emitted into the atmosphere in the exhaust gas. Marine vessels typically uses lean burn combustion engines and lower grade fuels that both results in high levels of SOx and particles in the exhaust gas. SOx is a result of combustion of sulphur containing compounds that are especially abundant in low-grade fuels.
The content of SOx may be reduced by one or more of a plurality of well-known technologies, or by using higher-grade fuels. Higher-grade fuels are, however, far more expensive than normal low-grade fuels.
Seawater scrubbers or more generally wet gas scrubbers are known for reduction of SOx and particles. To obtain a sufficient reduction of SOx and particles to meet international and national requirements, packed bed scrubbers are suggested/marketed by most of the suppliers of such equipment. Wet scrubbers without packing for increasing the contact area between gas and liquid have so far not been found to be as efficient packed bed scrubbers.
Common for the known processes that are efficient in removing SOx and particles with a sufficient efficiency to obtain a treated exhaust gas fulfilling the requirements, is that the equipment needed is heavy and space consuming in addition to reducing the efficiency of the engine output substantially and thereby increasing the running cost of the vessel.
Space and weight is always a problem in a marine vessel, as space consuming and heavy equipment will take up valuable space onboard and displace paying guests.
Due to the size of the existing solutions for wet scrubbing for reduction of SOx and particles to acceptable levels, the installation of the equipment will require substantial reconstruction of parts of the interior of the vessel, and may require the vessel to be taken out of service for a substantial period.
For state of the art packed bed scrubbers, as mentioned above, a bypass for exhaust has to be provided if water flow is stopped, as packed bed scrubbers should not be run dry.
Accordingly, the known solutions are not optimal for new projects and are very expensive to install in an existing vessel.
An object of the present invention is to provide a solution that is a good option for new projects due to the advantages given, and that is easy to install on an existing vessel where it is not required to take the vessel out of service for a long period, if at all.